Sweet potato protein

Tuber roots, their products and by-products Sugarbeet pulp, dried beet, potato, sweet potato as tuber, manioc as roots, potato pulp (byproduct of the extraction of potato starch), potato starch, potato protein and tapioca... 

Dog gastric lipase CaMV enhanced 35S promoter/ CaMV 35S terminator LP of rabbit gastric lipase precursor LP of sweet potato sporamin precursor N. tabacum (leaves secretion) N. tabacum (leaves vacuole) 7% of acid extractable proteins 5% of acid extractable proteins 51... 

Because composition and nutritional properties of the major food legumes and oilseeds have been reported in numerous technical journals and books (listed above), the section devoted to composition and chemistry highlights lesser-known but potentially important sources of plant protein that have not received the same attention. Some of these food crops have been cultivated for many years so that they are not "new" sources. Such crops as winged bean, sweet potato, tropical seeds, fruits and leaves, yams and cucurbits are potential sources of protein in areas where they are grown. These are discussed in greater detail in the remaining five chapters. 

Data are not available for protein production worldwide. However, an estimate of the protein contribution provided by sweet potatoes can be made if we assume a mean dry matter content of 28% and a mean protein content of 5%. Based on these assumptions, the sweet potato provides 1.92 million metric tons of protein worldwide. The yield of protein would be 134 kg/ha using worldwide yield values or 184 kg/ha using US production values. 

For those sweet potato cultivars studied, the crude protein (N x 6.25) contains both protein and nonprotein nitrogen (NPN). 

The initial report on the nature of sweet potato protein indicated that most of the protein was a globulin "ipomoein"... 

Sweet potato protein is unequally distributed within the... 

It would appear that commercial quantities of sweet potato protein might be readily available as a by-product of the starch industry. The laboratory concentrates were bland, light-colored powders containing 80-88% protein. 

Table I. Crude Protein Content (% Fresh Sweet Potato) of Ten Cultivars From Upper Mendi Grown in Different oo...

Feeding studies. Although sweet potatoes are a significant source of calories in many parts of the world, very little information is available concerning the nutritional quality of sweet potato protein as determined by controlled feeding studies in humans. 

Research by other workers ( 2, 33.) also suggested the sweet potato protein is readily utilized by humans. 

A report by Bressani et al. (3J7), which evaluated the nutritional value of diets based on starchy foods and beans, indicated that for the rat, sweet potato protein was of poor nutritional quality. When methionine was added to all diets to raise sulfur amino acids, sweet potato still required the largest amount of supplementation with bean flour to maintain animal weight (Table II). 

Sweet potato flour contained 3.8% protein, the second highest amount of protein among starchy foods, and yet the protein appeared to be the poorest in nutritional quality. However, it should be noted that the sweet potatoes used in this study were dried at 60 C but were not cooked. Uncooked sweet potato starch is not completely digestable by rodents. As a consequence, maintenance requirements would increase. This is the most likely explanation for the increased requirement for bean flour, but there also may have been interference with digestion from protease inhibitors present in uncooked sweet potatoes. 

Walter et al. (38) measured the protein efficiency ratio (PER) of flour prepared from sweet potatoes which were cooked in a drying oven. Because the PER is determined on the basis of a diet containing 10% protein, the Jewel and Centennial sweet potatoes used in this study were stored until sufficient starch had metabolized to increase crude protein content to 11.25% (dry basis). When the flour was fed to Sprague-Dawley strain rats, the corrected PER values were 2.22 and 2.00 for Centennial and Jewel cultivars, respectively, compared to 2.50 for casein. Centennial had the highest PER value of the two cultivars because its NPN content was lower. The net effect of increased NPN content is to lower the amount of essential amino acids as a percentage of the total nitrogen and thus decrease the PER value. 

Enteritis necrotians (EN), a spontaneous form of enteric gangrene endemic to the highlands of Papua, New Guinea, is caused by toxins produced when Clostridium perfringens of the gut enter a rapid growth phase (41). It has been postulated that the disease occurs in populations which consume a low protein diet, e.g., sweet potato as the staple food combined with TI activity which... 

In recent years, a number of workers have published amino acid analyses of the sweet potato (38, 43, 35, 22, 18). The overall picture is that the sweet potato amino acid pattern is of good nutritional quality but that the variability of individual amino acids both within the same cultivar and across cultivars is very high. For example, Walter et al. (44) reported that with the exception of aromatic amino acids, every essential amino acid has a score of less than 100 in one or more cultivars. The amino acid score is defined as the g of amino acid in 100 g of test protein divided by the number of g of that amino acid in the FAO/WHO reference pattern times 100. Bradbury et al. (22) showed that, for the same cultivar, environmental effects on the amino acid patterns is significant. For three cultivars, they found a mean percent standard deviation for all amino acids of 24.2,... 

The literature on concentrated sweet potato protein is sparse. Amino acid patterns for sweet potato protein isolates have been reported by three groups (16, 45, 46). One report showed that when compared to the FAO standard (47), no amino acids were limiting. The other reports showed total sulfur amino acids and lysine to be limiting (Table III). The patterns indicate a nutritionally well balanced protein. The improvement in nutritional quality, when compared to amino acid patterns from whole sweet potato, is due to the fact that whole sweet potatoes contain substantial amounts of NPN, which consists mainly of nonessential amino acids. This effectively dilutes the EAA and lowers the amino acid score. 

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